Inserting as fast as I can.

SqlBulkInsert.cs

using System.Data;
using System.Data.SqlClient;

internal class Program
{
    static int threads = 0;
    static int records = 0;
    static int batch = 10_000;
    static DateTime started = DateTime.Now;

    private static void Main(string[] args)
    {
        var db = "MyDemoDatabase";

        ExecuteSql($"""
            IF NOT EXISTS(SELECT 1 FROM sys.databases WHERE NAME = '{db}') 
                CREATE DATABASE {db};
            USE {db};
            DROP TABLE IF EXISTS Reading;
            CREATE TABLE[dbo].[Reading] 
            (
                  [Id][int] PRIMARY KEY NONCLUSTERED IDENTITY(1,1) NOT NULL
                , [Sensor] [int] NOT NULL
                , [Date] [datetimeoffset] (7) NOT NULL
                , [Value] [decimal](18, 0) NOT NULL
            );
        """, "master");

        _ = new Timer(x =>
        {
            Console.SetCursorPosition(0, 0);
            var seconds = (DateTime.Now - started).TotalSeconds;
            var rate = records / seconds;
            var million = 1_000_000 / rate;
            Console.WriteLine($"{seconds:#,#} seconds so far");
            Console.WriteLine($"{threads:#,#} active threads");
            Console.WriteLine($"{batch:#,#} batch size");
            Console.WriteLine($"{records:#,#} records inserted");
            Console.WriteLine($"{rate:#,#} inserted per second");
            Console.WriteLine($"1 million records in {million:#,#} seconds.");
        }, default, TimeSpan.Zero, TimeSpan.FromSeconds(1));

        Parallel.For(0, 100, i =>
        {
            Interlocked.Increment(ref threads);
            StartWriting(i, db);
            Interlocked.Decrement(ref threads);
        });

        Console.WriteLine("Done");
        Console.ReadLine();
    }

    static void StartWriting(int sensor, string db)
    {
        using SqlConnection connection = ConnectSql(db);

        while (connection.State == System.Data.ConnectionState.Open)
        {
            using var bulkCopy = new SqlBulkCopy(connection);

            var dataTable = GenerateData(batch);
            bulkCopy.DestinationTableName = dataTable.TableName;
            bulkCopy.BulkCopyTimeout = 0;
            bulkCopy.WriteToServer(dataTable);

            Interlocked.Add(ref records, dataTable.Rows.Count);
            Thread.Sleep(10);
        }

        DataTable GenerateData(int rows)
        {
            var dataTable = new DataTable("Reading");
            dataTable.Columns.Add(new DataColumn("Id", typeof(int)));
            dataTable.Columns.Add(new DataColumn("Sensor", typeof(int)));
            dataTable.Columns.Add(new DataColumn("Date", typeof(DateTime)));
            dataTable.Columns.Add(new DataColumn("Value", typeof(int)));

            for (int i = 0; i < rows; i++)
            {
                var row = dataTable.NewRow();
                row["Sensor"] = sensor;
                row["Date"] = DateTime.Now;
                row["Value"] = Random.Shared.Next();
                dataTable.Rows.Add(row);
            }

            return dataTable;
        }
    }

    static int ExecuteSql(string sql, string db)
    {
        using SqlConnection connection = ConnectSql(db);
        using SqlCommand command = connection.CreateCommand();
        command.CommandText = sql;
        return command.ExecuteNonQuery();
    }

    private static SqlConnection ConnectSql(string db)
    {
        var connectionString = $"Server=(localdb)\\MSSQLLocalDB;Integrated Security=true;database={db}";
        var connection = new SqlConnection(connectionString);
        connection.Open();
        return connection;
    }
}